1. Field of the Invention
The present invention relates to a pressing mold for optical lenses, a glass optical lens, a method for manufacturing glass optical lenses and the like.
2. Related art of the Invention
Conventionally, in order to manufacture a fine optical element with high accuracy, methods by processing resin directly or forming, since the processes are easy, have been adopted (see Japanese Patent Application Laid-Open (kokai) No. S54-110857 and Japanese Patent Publication (kokoku) No. S60-025761, for example).
However, such a fine optical element made of resin has a disadvantage that the accuracy tends to degrade since the shape is deformed because the volume of the resin changes due to environmental changes in temperature, humidity and the like. In addition, since the strength of the resin is low, the element has a disadvantage that the surface is easily damaged. Thus a reliable fine optical element with extremely high accuracy, which is made of resin, has not been obtained.
In contrast, a fine optical element made of glass has high durability; the surface is not easily damaged, and the accuracy does not degrade due to environmental changes. A method for manufacturing glass fine optical elements, by performing directly dry etching of the glass to process patterned fine optical elements, has been proposed (see, Japanese Patent Application Laid-Open (kokai) No. S55-057807, for example).
Such a method of processing glass by dry etching is capable of directly patterning the surface of the glass for the fine optical element, but has a disadvantage that, since it takes a lot of time to manufacture one element, many fine optical elements with the same pattern cannot be manufactured. Accordingly, by such methods, reliable glass fine optical elements with extremely high accuracy have not been mass-produced.
On the other hand, recently, methods for mass-producing optical glass elements (aspherical glass lenses, for example) by press molding of the glass have been proposed. When it becomes possible to produce glass optical lenses by repeated press molding of the glass, reliable fine optical elements with extremely high accuracy can be mass-produced. However, since high quality is required for a glass optical lens to produce image formation, in order to manufacture glass optical lenses by press molding, a pressing mold for high-accuracy glass optical lenses, which has extremely high strength and durability, is needed.
Materials of such molds are required to be excellent in heat shock resistance for molding performed repeatedly, and in processability for ultra-precise process; the materials are required to be chemically inactive with the glass even at higher temperature; the portion, which is to be a surface for forming the glass, has to be sufficiently hard and is not allowed to be easily damaged by friction and the like; the forming surface has to be free from plastic deformation and grain growth due to the molding at higher temperature.
As a mold material satisfying these necessary conditions to some extent, SiC material (see, Japanese Patent Application Laid-Open (kokai) No. S52-045613, for example) is proposed. Also, a mold having a cemented carbide mother material coated with a platinum group alloy thin film (see, Japanese Patent Application Laid-Open (kokai) No. S60-246230, for example) is proposed.
For press molding, a carbon-system thin film (a DLC film, for example) or a platinum-system alloy thin film is formed by sputtering on the patterned surface of such a mold with SiC material or cemented carbide material so that the demoldability of the glass may be improved.